1. Field of the Invention
The present invention relates to a method and system, for obtaining core samples during the drilling phase of wells, such as hydrocarbon wells and the like, by making use of a coring or encapsulating fluid.
2. Description of the Related Art
Particular reference will be made below to drilling of hydrocarbon wells, in the oil sector, but it is obvious that the invention can be extended to any field of application in which it might be necessary to obtain core samples during the drilling phase.
As is known, during drilling of a well, core samples must be obtained at predetermined depths intervals, that is samples of underground formations must be collected in order to carry out the necessary analyses at the surface to ascertain the type of rock that is being penetrated and identify any traces of hydrocarbon mineralisation, detection of which is the main purpose of well drilling.
According to the current methodology, coring operations take place according to the sequence below:
drilling is suspended PA1 mud is circulated in the well for a long enough period to ensure that formation fluids do not enter the bore hole PA1 the rotating drill pipes are lifted to the surface PA1 a special piece of equipment called a corer or core barrel is assembled ready PA1 the corer is lowered to bottom-hole by means of the pipes PA1 coring is carried out PA1 the corer is lifted to the surface PA1 the cores are collected.
The main aim of the invention is to allow collection of "cores" from bottom-of the well, avoiding performance of the work steps listed above and in particular avoiding removal of the rotating pipes from the well.
In the present state of the art of drilling, rock debris produced by the chipping action of the drill bit, which will be referred to henceforth by the English term "cuttings", are lifted from the well bottom to the surface by the circulation of so-called drilling mud, which, being pumped continually, travels downwards inside the constantly rotating drill pipes, then out through nozzles placed on the drill bit, to return upwards along the hollow annular space existing between the drill pipes and the hole bored by the bit.
Thus, the well bottom is continually cleaned, cuttings are removed and lifted to the surface, where they are collected for sampling and analysis at predetermined intervals during drilling.
With such a method, the cuttings carried to the surface from the well bottom are in direct contact with the mud that carries them upwards and obviously undergo more or less thorough washing which, though not altering their geological nature, nevertheless masks and makes uncertain the identification of fluid in the formation (water, oil, gas), thus eliminating any practical possibility of a qualitative and quantitative interpretation that would have been highly desirable.